The present invention was conceived and developed under a U.S. Government Contract awarded by the U.S. Department of Energy. The Government has rights in this invention.
The present invention is directed to silver/palladium (AgPd) cells. More particularly, the present invention is directed to AgPd cells used for adjusting or measuring a level of hydrogen in a high pressure environment, a high temperature environment and/or an environment incompatible with stainless steel. The present invention is also directed to methods of using such cells.
One of the properties of palladium is its ability, at room temperature, to absorb up to 900 times its own volume of hydrogen. This unique property has made palladium useful in controlling and monitoring hydrogen. Of special interest is the ability to use palladium as a hydrogen diffusion membrane across a pressure boundary. Silver-palladium (AgPd) cells have been manufactured for this purpose. By controlling the partial pressure of hydrogen in the AgPd cell external to the pressure boundary, it is possible to control the hydrogen levels inside a pressure boundary. A higher partial pressure of hydrogen on the exterior will allow diffusion of hydrogen across the AgPd cell and into a pressure vessel until equilibrium is achieved. Conversely, a lower partial pressure of hydrogen on the exterior side will allow hydrogen to xe2x80x9cventxe2x80x9d across the pressure boundary and into the pressure vessel. The AgPd cell can also be used to monitor hydrogen levels within a pressure vessel. A vacuum is pulled on the exterior of the AgPd cell. As hydrogen diffuses through the AgPd cell, the pressure on the exterior of the cell will reach an equilibrium. From a pressure reading from the inside of the cell, the hydrogen level within the pressure boundary can be calculated. While existing AgPd cells have been used to both control and monitor hydrogen levels across a pressure boundary, there are operational limitations on their usage.
One prior art AgPd cell consists of a thin 25% Ag/75% Pd tube supported internally by a cylindrical stainless steel xe2x80x9csponge.xe2x80x9d One end of the tube is sealed by brazing on a 304 stainless steel end cap. The other end of the tube is brazed onto a 304 stainless steel Swagelok fitting. The use of stainless steel unsatisfactorily limits the environments in which AgPd cells can be used. For example, a caustic environment might corrode stainless steel if such a cell were used.
Another prior art AgPd cell consists of a 20% Ag/80% Pd tube with a welded end. This tube has only a 0.060 inch thickness and is rated to withstand pressures of up to only 2,000 p.s.i. This pressure rating unsatisfactorily limits the environments in which this prior art cell may be used. Attempts to manufacture an operable AgPd tube with a greater wall thickness have been unsuccessful.
Those skilled in the art will recognize that there is a need for a AgPd cell with improved operating characteristics, as well as a need for methods using such a AgPd cell. A further need in the art is a AgPd cell that is operable at higher pressures and/or higher temperatures, as well as a need for methods using such a AgPd cell. A still further need in the art is a AgPd cell that is operable in environments that are incompatible with stainless steel, as well as a need for methods using such a AgPd cell.
It is therefore a primary object of the invention to provide a AgPd cell and methods of measuring or adjusting a level of hydrogen that meet these needs in the art.
I have discovered that one or more of these needs is met by a AgPd cell comprising a hollow diffusion tube made of a AgPd alloy, a hollow connecting member having first and second ends, and a hollow connecting tube. The diffusion tube has a closed end and an open end. The first end of the hollow connecting member is operably associated with the open end of the hollow diffusion tube. The hollow connecting tube is operably associated with the second end of the hollow connecting member. The cell is operable at pressures up to and including about 3,600 p.s.i.
A AgPd cell, according to another aspect of the invention, comprises a hollow diffusion tube made of a AgPd alloy, a hollow connecting member having first and second ends, and a hollow connecting tube. The diffusion tube has a closed end and an open end. The first end of the hollow connecting member is operably associated with the open end of the hollow diffusion tube. The hollow connecting tube is operably associated with the second end of the hollow connecting member. The cell is operable at pressures up to and including about 2,600 p.s.i. and at temperatures up to and including about 338 degrees Celsius.
A AgPd cell, according to another aspect of the invention, comprises a hollow diffusion tube made of a AgPd alloy, a hollow connecting member having first and second ends, and a hollow connecting tube. The diffusion tube has a closed end and an open end. The first end of the hollow connecting member is operably associated with the open end of the hollow diffusion tube. The hollow connecting tube is operably associated with the second end of the hollow connecting member. The cell is operable at a hollow diffusion tube wall thickness greater than 0.060 inches and less than or equal to 0.089 inches.
A method of measuring a level of hydrogen in an environment outside a AgPd cell, according to another aspect of the invention, comprises the following steps. A AgPd cell is provided. A level of hydrogen in an environment outside the AgPd cell is measured by allowing hydrogen to diffuse into or out of the AgPd cell, wherein the environment has a pressure up to and including 3,600 p.s.i. The AgPd cell comprises a hollow diffusion tube, a hollow connecting member, a hollow connecting tube, and a pressure sensor for measuring a level of hydrogen. The hollow diffusion tube is made of a AgPd alloy and has a closed end and an open end. The hollow connecting member has first and second ends, wherein the first end is operably associated with the open end of the hollow diffusion tube. The hollow connecting tube is operably associated with the second end of the hollow connecting member. The pressure sensor is operably associated with the hollow connecting tube.
A method of adjusting a level of hydrogen in an environment outside a AgPd cell, according to yet another aspect of the invention, comprises the following steps. A source of hydrogen is provided. A AgPd cell is provided. The level of hydrogen in an environment outside the AgPd cell is increased or decreased by increasing or decreasing the level of hydrogen from the hydrogen source to the AgPd cell, wherein the environment is at a pressure up to and including about 3,600 p.s.i. The AgPd cell comprises a hollow diffusion tube, a hollow connecting member, and a hollow connecting tube. The hollow diffusion tube is made of a AgPd alloy and has a closed end and an open end. The hollow connecting member has first and second ends, wherein the first end is operably associated with the open end of the hollow diffusion tube. The hollow connecting tube is operably associated with the second end of the hollow connecting member.